When did Joss said death was a main theme of them? He said it was darker but I haven't read anything about death let alone major character death. Stakes can be major without main characters dying. The stakes for heroes should be about saving the world - not just saving it because someone they know died so now it's important. That doesn't sound very heroic. That's why I always thought the Coulson bit in The Avengers was completely unnecessary. Comparisons have been made to it being darker like Empire Strikes Back. No one dies in ETS - not even the robots. Solo get frozen but he isn't any more dead at the end than Steve is at the end of Captain America. Besides if as rumored they're all to a certain degree responsible for Ultron being created the stakes are already personal as is the guilt.